In order to rotate a rotating electric machine (a motor, a generator or a motor-and-generator) under severe load conditions or to reduce the size of the rotating electric machine, it is necessary to quickly radiate heat generated at a coil or a stator core. If the temperature of a stator increases, enamel coating of an enamel line of the coil or insulating paper insulating the coil from the stator could be burned out.
Recently, vehicles using a rotating electric machine as a driving source together with or in place of an engine, such as an electric vehicle, a hybrid vehicle and a fuel cell vehicle have been introduced. Particularly heavy requirements of driving under severe load conditions and size reduction are imposed on the rotating electric machine mounted on such a vehicle.
In the conventional art, a technique of directly applying cooling liquid to a coil winding portion to lower coil temperature and to prevent burnout of the enamel coating or insulating paper has been known. By way of example, a cooling liquid supply port is provided at an upper portion of a case housing the rotating electric machine, and the cooling liquid is sprayed to the coil through the cooling liquid supply port for cooling the coil.
When the cooling liquid is supplied to the coil and then let fall by gravitation, only about 30 to about 60% of the outer surface area of the coil could actually be covered with the cooling liquid, and the remaining portions of the coil surface are not wet by the cooling liquid but are cooled with air. Therefore, though the coil temperature becomes lower than when the entire surface area of the coil is cooled with air, the coil temperature increases in a range of severer driving conditions (high speed range or large torque range).
Japanese Patent Laying-Open Nos. 2002-272041, 4-364343, 2003-289650 and 2003-224945 disclose a rotating electric machine having a closed type cooling flow passage provided on an end surface of a coil winding portion of a stator. Such a structure improves the effect of cooling the coil than when the cooling liquid is simply sprayed to the coil and the liquid flows down as determined by gravitation.
In the structure disclosed in the prior art references such as Japanese Patent Laying-Open No. 2002-272041, however, the cooling liquid is supplied from an upper portion of the rotating electric machine and discharged at a lower portion. In such a structure, if the supply of cooling liquid is insufficient, the cooling liquid may locally fail to contact even with the portion on the coil winding end surface, and hence, cooling performance is not satisfactory.